Increase in-service time and robustness for sustained mobility in idle mode

ABSTRACT

Wireless communications systems and methods related to user equipment (UE) idle mode mobility in a wireless communication network are provided. A wireless communication device establishes a network session with a wireless communication network. The wireless communication device reselects a first cell for camping, wherein the first cell is associated with the wireless communication network. The wireless communication device monitors for first system information from the first cell. The wireless communication device reselects a second cell for camping in response to a failure to receive the first system information. The second cell is associated with the wireless communication network and different from the first cell. The wireless communication device maintains the network session during the reselecting the first cell for camping and the reselecting the second cell for camping.

TECHNICAL FIELD

This application relates to wireless communication systems, and moreparticularly to user equipment (UE) idle mode mobility in a wirelesscommunication network.

INTRODUCTION

Wireless communications systems are widely deployed to provide varioustypes of communication content such as voice, video, packet data,messaging, broadcast, and so on. These systems may be capable ofsupporting communication with multiple users by sharing the availablesystem resources (e.g., time, frequency, and power). A wirelessmultiple-access communications system may include a number of basestations (BSs), each simultaneously supporting communications formultiple communication devices, which may be otherwise known as userequipment (UE).

To meet the growing demands for expanded mobile broadband connectivity,wireless communication technologies are advancing from the long termevolution (LTE) technology to a next generation new radio (NR)technology. For example, NR is designed to provide a lower latency, ahigher bandwidth or a higher throughput, and a higher reliability thanLTE. NR is designed to operate over a wide array of spectrum bands, forexample, from low-frequency bands below about 1 gigahertz (GHz) andmid-frequency bands from about 1 GHz to about 6 GHz, to high-frequencybands such as millimeter wave (mmWave) bands. NR is also designed tooperate across different spectrum types, from licensed spectrum tounlicensed and shared spectrum. Spectrum sharing enables operators toopportunistically aggregate spectrums to dynamically supporthigh-bandwidth services. Spectrum sharing can extend the benefit of NRtechnologies to operating entities that may not have access to alicensed spectrum.

Maintaining mobility is important in a wireless communication network,where a UE may travel from one coverage area or cell to another coveragearea or cell. In general, a UE may be in an idle state or a connectedstate with respect to a network. An idle mode UE is not attached to anyBS and there are no network and/or radio resources allocated to the UE.The UE's location is known to the network, for example, within a groupof cells referred to as a tracking area. While a UE is not attached toany BS, the UE is required to select a suitable cell to camp on. Theprocedure of a UE selecting and camping on a cell is referred to as cellselection. While camping on a cell, the UE continues to monitor othercells. When the UE detects a degradation in the received signal qualityfrom the currently camped cell, for example, due to mobility, the UE maydecide to camp on another cell. The procedure of evaluating andreselecting another cell while the UE is currently camped on a servingcell is referred to as cell reselection.

BRIEF SUMMARY OF SOME EXAMPLES

The following summarizes some aspects of the present disclosure toprovide a basic understanding of the discussed technology. This summaryis not an extensive overview of all contemplated features of thedisclosure, and is intended neither to identify key or critical elementsof all aspects of the disclosure nor to delineate the scope of any orall aspects of the disclosure. Its sole purpose is to present someconcepts of one or more aspects of the disclosure in summary form as aprelude to the more detailed description that is presented later.

For example, in an aspect of the disclosure, a method of wirelesscommunication, comprising establishing, by a wireless communicationdevice, a network session with a wireless communication network;reselecting, by the wireless communication device, a first cell forcamping, wherein the first cell is associated with the wirelesscommunication network; monitoring, by the wireless communication device,for first system information from the first cell; reselecting, by thewireless communication device, a second cell for camping in response toa failure to receive the first system information, wherein the secondcell is associated with the wireless communication network and differentfrom the first cell; and maintaining, by the wireless communicationdevice, the network session during the reselecting the first cell forcamping and the reselecting the second cell for camping.

In an additional aspect of the disclosure, an apparatus comprising aprocessor configured to establish a network session with a wirelesscommunication network; reselect a first cell for camping, wherein thefirst cell is associated with the wireless communication network;monitor for first system information from the first cell; reselect asecond cell for camping in response to a failure to receive the firstsystem information, wherein the second cell is associated with thewireless communication network and different from the first cell; andmaintain the network session during the reselecting the first cell forcamping and the reselecting the second cell for camping.

In an additional aspect of the disclosure, a non-transitorycomputer-readable medium having program code recorded thereon, theprogram code comprising code for causing a wireless communication deviceto establish a network session with a wireless communication network;code for causing the wireless communication device to reselect a firstcell for camping, wherein the first cell is associated with the wirelesscommunication network; code for causing the wireless communicationdevice to monitor for first system information from the first cell; codefor causing the wireless communication device to reselect a second cellfor camping in response to a failure to receive the first systeminformation, wherein the second cell is associated with the wirelesscommunication network and different from the first cell; and code forcausing the wireless communication device to maintain the networksession during the reselecting the first cell for camping and thereselecting the second cell for camping.

Other aspects, features, and embodiments of the present invention willbecome apparent to those of ordinary skill in the art, upon reviewingthe following description of specific, exemplary embodiments of thepresent invention in conjunction with the accompanying figures. Whilefeatures of the present invention may be discussed relative to certainembodiments and figures below, all embodiments of the present inventioncan include one or more of the advantageous features discussed herein.In other words, while one or more embodiments may be discussed as havingcertain advantageous features, one or more of such features may also beused in accordance with the various embodiments of the inventiondiscussed herein. In similar fashion, while exemplary embodiments may bediscussed below as device, system, or method embodiments it should beunderstood that such exemplary embodiments can be implemented in variousdevices, systems, and methods.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wireless communication network according to someembodiments of the present disclosure.

FIG. 2 illustrates a wireless communication network according to someembodiments of the present disclosure.

FIG. 3 is a signaling diagram illustrating a cell selection and cellreselection method according to embodiments of the present disclosure.

FIG. 4 is a block diagram of a user equipment (UE) according to someembodiments of the present disclosure.

FIG. 5 is a block diagram of an exemplary base station (BS) according tosome embodiments of the present disclosure.

FIG. 6 is a flow diagram of a cell reselection method with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure.

FIG. 7 is a flow diagram of a cell reselection method with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure.

FIG. 8 is a flow diagram of a cell reselection method with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure.

FIG. 9 is a flow diagram of a cell reselection method with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure.

FIG. 10 is a time diagram illustrating a mobility scenario with fastcell reselections according to some embodiments of the presentdisclosure.

FIG. 11 is a flow diagram of a cell reselection method with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure.

DETAILED DESCRIPTION

The detailed description set forth below, in connection with theappended drawings, is intended as a description of variousconfigurations and is not intended to represent the only configurationsin which the concepts described herein may be practiced. The detaileddescription includes specific details for the purpose of providing athorough understanding of the various concepts. However, it will beapparent to those skilled in the art that these concepts may bepracticed without these specific details. In some instances, well-knownstructures and components are shown in block diagram form in order toavoid obscuring such concepts.

This disclosure relates generally to wireless communications systems,also referred to as wireless communications networks. In variousembodiments, the techniques and apparatus may be used for wirelesscommunication networks such as code division multiple access (CDMA)networks, time division multiple access (TDMA) networks, frequencydivision multiple access (FDMA) networks, orthogonal FDMA (OFDMA)networks, single-carrier FDMA (SC-FDMA) networks, LTE networks, GSMnetworks, 5^(th) Generation (5G) or new radio (NR) networks, as well asother communications networks. As described herein, the terms “networks”and “systems” may be used interchangeably.

An OFDMA network may implement a radio technology such as evolved UTRA(E-UTRA), Institute of Electrical and Electronics Engineers (IEEE)802.11, IEEE 802.16, IEEE 802.20, flash-OFDM and the like. UTRA, E-UTRA,and Global System for Mobile Communications (GSM) are part of universalmobile telecommunication system (UMTS). In particular, long termevolution (LTE) is a release of UMTS that uses E-UTRA. UTRA, E-UTRA,GSM, UMTS and LTE are described in documents provided from anorganization named “3rd Generation Partnership Project” (3GPP), andcdma2000 is described in documents from an organization named “3rdGeneration Partnership Project 2” (3GPP2). These various radiotechnologies and standards are known or are being developed. Forexample, the 3rd Generation Partnership Project (3GPP) is acollaboration between groups of telecommunications associations thataims to define a globally applicable third generation (3G) mobile phonespecification. 3GPP long term evolution (LTE) is a 3GPP project whichwas aimed at improving the UMTS mobile phone standard. The 3GPP maydefine specifications for the next generation of mobile networks, mobilesystems, and mobile devices. The present disclosure is concerned withthe evolution of wireless technologies from LTE, 4G, 5G, NR, and beyondwith shared access to wireless spectrum between networks using acollection of new and different radio access technologies or radio airinterfaces.

In particular, 5G networks contemplate diverse deployments, diversespectrum, and diverse services and devices that may be implemented usingan OFDM-based unified, air interface. In order to achieve these goals,further enhancements to LTE and LTE-A are considered in addition todevelopment of the new radio technology for 5G NR networks. The 5G NRwill be capable of scaling to provide coverage (1) to a massive Internetof things (IoTs) with an ultra-high density (e.g., ˜1M nodes/km²),ultra-low complexity (e.g., ˜10s of bits/sec), ultra-low energy (e.g.,˜10+ years of battery life), and deep coverage with the capability toreach challenging locations; (2) including mission-critical control withstrong security to safeguard sensitive personal, financial, orclassified information, ultra-high reliability (e.g., ˜99.9999%reliability), ultra-low latency (e.g., ˜1 ms), and users with wideranges of mobility or lack thereof; and (3) with enhanced mobilebroadband including extreme high capacity (e.g., ˜10 Tbps/km²), extremedata rates (e.g., multi-Gbps rate, 100+ Mbps user experienced rates),and deep awareness with advanced discovery and optimizations.

The 5G NR may be implemented to use optimized OFDM-based waveforms withscalable numerology and transmission time interval (TTI); having acommon, flexible framework to efficiently multiplex services andfeatures with a dynamic, low-latency time division duplex(TDD)/frequency division duplex (FDD) design; and with advanced wirelesstechnologies, such as massive multiple input, multiple output (MIMO),robust millimeter wave (mmWave) transmissions, advanced channel coding,and device-centric mobility. Scalability of the numerology in 5G NR,with scaling of subcarrier spacing, may efficiently address operatingdiverse services across diverse spectrum and diverse deployments. Forexample, in various outdoor and macro coverage deployments of less than3 GHz FDD/TDD implementations, subcarrier spacing may occur with 15 kHz,for example over 1, 5, 10, 20 MHz, and the like bandwidth (BW). Forother various outdoor and small cell coverage deployments of TDD greaterthan 3 GHz, subcarrier spacing may occur with 30 kHz over 80/100 MHz BW.For other various indoor wideband implementations, using a TDD over theunlicensed portion of the 5 GHz band, the subcarrier spacing may occurwith 60 kHz over a 160 MHz BW. Finally, for various deploymentstransmitting with mmWave components at a TDD of 28 GHz, subcarrierspacing may occur with 120 kHz over a 500 MHz BW.

The scalable numerology of the 5G NR facilitates scalable TTI fordiverse latency and quality of service (QoS) requirements. For example,shorter TTI may be used for low latency and high reliability, whilelonger TTI may be used for higher spectral efficiency. The efficientmultiplexing of long and short TTIs to allow transmissions to start onsymbol boundaries. 5G NR also contemplates a self-contained integratedsubframe design with uplink/downlink scheduling information, data, andacknowledgement in the same subframe. The self-contained integratedsubframe supports communications in unlicensed or contention-basedshared spectrum, adaptive uplink/downlink that may be flexiblyconfigured on a per-cell basis to dynamically switch between uplink anddownlink to meet the current traffic needs.

Various other aspects and features of the disclosure are furtherdescribed below. It should be apparent that the teachings herein may beembodied in a wide variety of forms and that any specific structure,function, or both being disclosed herein is merely representative andnot limiting. Based on the teachings herein one of an ordinary level ofskill in the art should appreciate that an aspect disclosed herein maybe implemented independently of any other aspects and that two or moreof these aspects may be combined in various ways. For example, anapparatus may be implemented or a method may be practiced using anynumber of the aspects set forth herein. In addition, such an apparatusmay be implemented or such a method may be practiced using otherstructure, functionality, or structure and functionality in addition toor other than one or more of the aspects set forth herein. For example,a method may be implemented as part of a system, device, apparatus,and/or as instructions stored on a computer readable medium forexecution on a processor or computer. Furthermore, an aspect maycomprise at least one element of a claim.

In a wireless communication network, a BS may broadcast systeminformation, for example, in the form of master information block (MIB)and system information blocks (SIBs). The system information includesessential or critical information, such as downlink (DL) channelconfiguration information, uplink (UL) channel configurationinformation, and access class information or cell barring information,for a UE to access the network. Certain system information may be moreimportant or critical than others for network access. Without asuccessful reception of the important or critical system information,the UE may not be able to continue to camp on a cell.

In some instances, a UE may attempt to camp on a cell continually havinga poor DL radio signal condition. Thus, the UE may be unable to receiveall the critical system information for a long period of time. In orderto avoid trying to receive the critical system information indefinitely,the UE may utilize certain timers to terminate the monitoring of thecritical system information. Upon expiration of the timers, UE may goout of service (OOS) and restart a cell selection to find a suitablecell for camping. Similarly, in some examples, when the UE fails toreceive non-critical system information within a certain time limit, theUE may also declare OOS and restart a cell selection. While the timeoutmechanisms allow the UE to stop monitoring for system information, therestarting of a cell selection can be time consuming and powerconsuming. In addition, the declaring of the OOS can cause the UE tomiss paging and/or calls.

The present application describes mechanisms for a UE to increasein-service time and improve idle mode mobility robustness. For example,a UE performs an initial cell selection to select a suitable cell forcamping in a network. After selecting a suitable or serving cell, the UEperforms a network attachment procedure to establish a network sessionwith the network. The UE monitors and evaluates signal measurements fromthe serving cell and neighboring cells while camping on the servingcell. The UE may select another cell for camping (e.g., due to mobility)and monitor for system information from the selected cell. In thedisclosed embodiments, upon failing to camp on the selected cell due toa failure to receive certain system information from the selected cell,the UE performs a fast cell reselection instead of declaring OOS andrestarting a time-consuming and/or power-consuming initial cellselection procedure as in a conventional UE procedure. In other words,the fast cell reselection is initiated based on a system informationreception failure instead of based on cell signal measurements as in aconventional cell reselection procedure. In addition, the UE canreselect to another cell without having to monitor signal measurementsfrom the cell for a certain duration and ensuring that the cell isbetter than the serving cell for the duration before the reselection,and thus providing a fast or immediate cell reselection. Further, thenetwork session is maintained while the UE performs the fast cellreselection, and thus can increase the amount of time the UE is inservice and reduces missed calls for the UE.

In an embodiment, during the fast cell reselection, the UE selects ahighest priority cell from among neighboring cells that satisfy certaincell reselection criteria. For example, the cell reselection criteriamay require the neighboring cells to have signal measurements higherthan signal measurements of the serving cell. When there are multipleneighboring cells with the same priority satisfying the cell reselectioncriteria, the UE selects the cell with signal measurements satisfyingthe cell reselection criteria for the longest duration or the cell withthe highest signal strength.

In an embodiment, when the UE determines that there is no neighboringcell satisfying the cell reselection criteria at the time of the fastcell reselection, the UE performs a one-shot signal measurement for eachavailable neighboring cell. In some instances, when nointer-frequency/inter-RAT neighboring lists were received (due to SIBreception failure), the UE may search for neighboring cells on theserving frequency. Alternatively, the UE may determine availableneighboring cells by searching databases of neighboring cells collectedbased on cell monitoring history and/or geographical locationinformation of the UE and neighboring cells. The UE selects the cellwith the highest priority and the highest signal measurement based onthe one-shot measurements. In an embodiment, when the neighboring cellsare mmWav cells, the UE performs signal measurements in a plurality ofbeam directions and selects the cell having the largest number of beamswith signal measurements above a certain threshold.

In an embodiment, the UE restricts the amount of time or the number ofattempts that the UE can perform a fast cell reselection, for example,by utilizing a combination of timers and counters. The UE can configurea maximum allowable time duration and/or a maximum allowable number ofattempts for fast cell reselection based on a critical level of themissing or failed system information. For example, the UE can allow fora longer duration and/or a greater number of retries for fast cellreselections when the missing or failed system information is lesscritical. Additionally, the UE may exclude a candidate cell from asubsequent cell selection or cell reselection if there are multiple pastor present critical and/or non-critical system information receptionand/or decoding failures from the candidate cell.

FIG. 1 illustrates a wireless communication network 100 according tosome embodiments of the present disclosure. The network 100 may be a 5Gnetwork. The network 100 includes a number of base stations (BSs) 105(individually labeled as 105 a, 105 b, 105 c, 105 d, 105 e, and 105 f)and other network entities. A BS 105 may be a station that communicateswith UEs 115 and may also be referred to as an evolved node B (eNB), anext generation eNB (gNB), an access point, and the like. Each BS 105may provide communication coverage for a particular geographic area. In3GPP, the term “cell” can refer to this particular geographic coveragearea of a BS 105 and/or a BS subsystem serving the coverage area,depending on the context in which the term is used.

A BS 105 may provide communication coverage for a macro cell or a smallcell, such as a pico cell or a femto cell, and/or other types of cell. Amacro cell generally covers a relatively large geographic area (e.g.,several kilometers in radius) and may allow unrestricted access by UEswith service subscriptions with the network provider. A small cell, suchas a pico cell, would generally cover a relatively smaller geographicarea and may allow unrestricted access by UEs with service subscriptionswith the network provider. A small cell, such as a femto cell, wouldalso generally cover a relatively small geographic area (e.g., a home)and, in addition to unrestricted access, may also provide restrictedaccess by UEs having an association with the femto cell (e.g., UEs in aclosed subscriber group (CSG), UEs for users in the home, and the like).A BS for a macro cell may be referred to as a macro BS. A BS for a smallcell may be referred to as a small cell BS, a pico BS, a femto BS or ahome BS. In the example shown in FIG. 1, the BSs 105 d and 105 e may beregular macro BSs, while the BSs 105 a-105 c may be macro BSs enabledwith one of three dimension (3D), full dimension (FD), or massive MIMO.The BSs 105 a-105 c may take advantage of their higher dimension MIMOcapabilities to exploit 3D beamforming in both elevation and azimuthbeamforming to increase coverage and capacity. The BS 105 f may be asmall cell BS which may be a home node or portable access point. A BS105 may support one or multiple (e.g., two, three, four, and the like)cells.

The network 100 may support synchronous or asynchronous operation. Forsynchronous operation, the BSs may have similar frame timing, andtransmissions from different BSs may be approximately aligned in time.For asynchronous operation, the BSs may have different frame timing, andtransmissions from different BSs may not be aligned in time.

The UEs 115 are dispersed throughout the wireless network 100, and eachUE 115 may be stationary or mobile. A UE 115 may also be referred to asa terminal, a mobile station, a subscriber unit, a station, or the like.A UE 115 may be a cellular phone, a personal digital assistant (PDA), awireless modem, a wireless communication device, a handheld device, atablet computer, a laptop computer, a cordless phone, a wireless localloop (WLL) station, or the like. In one aspect, a UE 115 may be a devicethat includes a Universal Integrated Circuit Card (UICC). In anotheraspect, a UE may be a device that does not include a UICC. In someaspects, the UEs 115 that do not include UICCs may also be referred toas IoT devices or internet of everything (IoE) devices. The UEs 115a-115 d are examples of mobile smart phone-type devices accessingnetwork 100. A UE 115 may also be a machine specifically configured forconnected communication, including machine type communication (MTC),enhanced MTC (eMTC), narrowband IoT (NB-IoT) and the like. The UEs 115e-115 k are examples of various machines configured for communicationthat access the network 100. A UE 115 may be able to communicate withany type of the BSs, whether macro BS, small cell, or the like. In FIG.1, a lightning bolt (e.g., communication links) indicates wirelesstransmissions between a UE 115 and a serving BS 105, which is a BSdesignated to serve the UE 115 on the downlink and/or uplink, or desiredtransmission between BSs, and backhaul transmissions between BSs.

In operation, the BSs 105 a-105 c may serve the UEs 115 a and 115 busing 3D beamforming and coordinated spatial techniques, such ascoordinated multipoint (CoMP) or multi-connectivity. The macro BS 105 dmay perform backhaul communications with the BSs 105 a-105 c, as well assmall cell, the BS 105 f. The macro BS 105 d may also transmitsmulticast services which are subscribed to and received by the UEs 115 cand 115 d. Such multicast services may include mobile television orstream video, or may include other services for providing communityinformation, such as weather emergencies or alerts, such as Amber alertsor gray alerts.

The BSs 105 may also communicate with a core network. The core networkmay provide user authentication, access authorization, tracking,Internet Protocol (IP) connectivity, and other access, routing, ormobility functions. At least some of the BSs 105 (e.g., which may be anexample of a gNB or an access node controller (ANC)) may interface withthe core network through backhaul links (e.g., NG-C, NG-U, etc.) and mayperform radio configuration and scheduling for communication with theUEs 115. In various examples, the BSs 105 may communicate, eitherdirectly or indirectly (e.g., through core network), with each otherover backhaul links (e.g., X1, X2, etc.), which may be wired or wirelesscommunication links.

The network 100 may also support mission critical communications withultra-reliable and redundant links for mission critical devices, such asthe UE 115 e, which may be a drone. Redundant communication links withthe UE 115 e may include links from the macro BSs 105 d and 105 e, aswell as links from the small cell BS 105 f. Other machine type devices,such as the UE 115 f (e.g., a thermometer), the UE 115 g (e.g., smartmeter), and UE 115 h (e.g., wearable device) may communicate through thenetwork 100 either directly with BSs, such as the small cell BS 105 f,and the macro BS 105 e, or in multi-hop configurations by communicatingwith another user device which relays its information to the network,such as the UE 115 f communicating temperature measurement informationto the smart meter, the UE 115 g, which is then reported to the networkthrough the small cell BS 105 f. The network 100 may also provideadditional network efficiency through dynamic, low-latency TDD/FDDcommunications, such as in a vehicle-to-vehicle (V2V)

In some implementations, the network 100 utilizes OFDM-based waveformsfor communications. An OFDM-based system may partition the system BWinto multiple (K) orthogonal subcarriers, which are also commonlyreferred to as subcarriers, tones, bins, or the like. Each subcarriermay be modulated with data. In some instances, the subcarrier spacingbetween adjacent subcarriers may be fixed, and the total number ofsubcarriers (K) may be dependent on the system BW. The system BW mayalso be partitioned into subbands. In other instances, the subcarrierspacing and/or the duration of TTIs may be scalable.

In an embodiment, the BSs 105 can assign or schedule transmissionresources (e.g., in the form of time-frequency resource blocks (RB)) fordownlink (DL) and uplink (UL) transmissions in the network 100. DLrefers to the transmission direction from a BS 105 to a UE 115, whereasUL refers to the transmission direction from a UE 115 to a BS 105. Thecommunication can be in the form of radio frames. A radio frame may bedivided into a plurality of subframes, for example, about 10. Eachsubframe can be divided into slots, for example, about 2. Each slot maybe further divided into mini-slots. In a FDD mode, simultaneous UL andDL transmissions may occur in different frequency bands. For example,each subframe includes a UL subframe in a UL frequency band and a DLsubframe in a DL frequency band. In a TDD mode, UL and DL transmissionsoccur at different time periods using the same frequency band. Forexample, a subset of the subframes (e.g., DL subframes) in a radio framemay be used for DL transmissions and another subset of the subframes(e.g., UL subframes) in the radio frame may be used for ULtransmissions.

The DL subframes and the UL subframes can be further divided intoseveral regions. For example, each DL or UL subframe may havepre-defined regions for transmissions of reference signals, controlinformation, and data. Reference signals are predetermined signals thatfacilitate the communications between the BSs 105 and the UEs 115. Forexample, a reference signal can have a particular pilot pattern orstructure, where pilot tones may span across an operational BW orfrequency band, each positioned at a pre-defined time and a pre-definedfrequency. For example, a BS 105 may transmit cell specific referencesignals (CRSs) and/or channel state information—reference signals(CSI-RSs) to enable a UE 115 to estimate a DL channel. Similarly, a UE115 may transmit sounding reference signals (SRSs) to enable a BS 105 toestimate a UL channel. Control information may include resourceassignments and protocol controls. Data may include protocol data and/oroperational data. In some embodiments, the BSs 105 and the UEs 115 maycommunicate using self-contained subframes. A self-contained subframemay include a portion for DL communication and a portion for ULcommunication. A self-contained subframe can be DL-centric orUL-centric. A DL-centric subframe may include a longer duration for DLcommunication than for UL communication. A UL-centric subframe mayinclude a longer duration for UL communication than for ULcommunication.

In an embodiment, the network 100 may be an NR network deployed over alicensed spectrum. The BSs 105 can transmit synchronization signals(e.g., including a primary synchronization signal (PSS) and a secondarysynchronization signal (SSS)) in the network 100 to facilitatesynchronization. The BSs 105 can broadcast system information associatedwith the network 100 (e.g., including a MIB, remaining minimum systeminformation (RMSI), and other system information (OSI)) to facilitateinitial network access. In some instances, the BSs 105 may broadcast thePSS, the SSS, and/or the MIB in the form of synchronization signalblocks (SSBs) over a physical broadcast channel (PBCH) and may broadcastthe RMSI and/or the OSI over a physical downlink shared channel (PDSCH).

In an embodiment, a UE 115 attempting to access the network 100 mayperform an initial cell search by detecting a PSS from a BS 105. The PSSmay enable synchronization of period timing and may indicate a physicallayer identity value. The UE 115 may then receive a SSS. The SSS mayenable radio frame synchronization, and may provide a cell identityvalue, which may be combined with the physical layer identity value toidentify the cell. The PSS and the SSS may be located in a centralportion of a carrier or any suitable frequencies within the carrier.

After receiving the PSS and SSS, the UE 115 may receive a MIB. The MIBmay include system information for initial network access and schedulinginformation for RMSI and/or OSI. After decoding the MIB, the UE 115 mayreceive RMSI and/or OSI. The RMSI and/or OSI may include radio resourcecontrol (RRC) information related to random access channel (RACH)procedures, paging, control resource set (CORESET) for physical downlinkcontrol channel (PDCCH) monitoring, physical uplink control channel(PUCCH), physical uplink shared channel (PUSCH), power control, and SRS.

After obtaining the MIB, the RMSI and/or the OSI, the UE 115 can performa random access procedure to establish a connection with the BS 105. Forthe random access procedure, the UE 115 may transmit a random accesspreamble and the BS 105 may respond with a random access response. Uponreceiving the random access response, the UE 115 may transmit aconnection request to the BS 105 and the BS 105 may respond with aconnection response (e.g., contention resolution message).

After establishing a connection, the UE 115 and the BS 105 can enter anormal operation stage, where operational data may be exchanged. Forexample, the BS 105 may schedule the UE 115 for UL and/or DLcommunications. The BS 105 may transmit UL and/or DL scheduling grantsto the UE 115 via a PDCCH. The BS 105 may transmit a DL communicationsignal to the UE 115 via a PDSCH according to a DL scheduling grant. TheUE 115 may transmit a UL communication signal to the BS 105 via a PUSCHand/or PUCCH according to a UL scheduling grant. The connection may bereferred to as an RRC connection. When the UE 115 is actively exchangingdata with the BS 105, the UE 115 is in an RRC connected state.

In an example, after establishing a connection with the BS 105, the UE115 may initiate an initial network attachment procedure with thenetwork 100. The BS 105 may coordinate with various network entities orfifth generation core (5GC) entities, such as a access and mobilityfunction (AMF), a serving gateway (SGW), and/or a packet data networkgateway (PGW), to complete the network attachment procedure. Forexample, the BS 105 may coordinate with the network entities in the 5GCto identify the UE, authenticate the UE, and/or authorize the UE forsending and/or receiving data in the network 100. In addition, the AMFmay assign the UE with a group of tracking areas (TAs), which may alsobe referred to as routing notification areas (RNAs). Once the networkattach procedure succeeds, a context is established for the UE 115 inthe AMF. After a successful attach to the network, the UE 115 can movearound the current TA. For tracking area update (TAU), the BS 105 mayrequest the UE 115 to update the network 100 with the UE 115's locationperiodically. Alternatively, the UE 115 may only report the UE 115'slocation to the network 100 when entering a new TA. The TAU allows thenetwork 100 to quickly locate the UE 115 and page the UE 115 uponreceiving an incoming data packet or call for the UE 115. When the UE115 has no active data communication with the BS 105 after the networkattachment, the UE 115 may return to an idle state (e.g., an RRC idlestate). During an idle state, the UE 115 may perform channelmeasurements, perform cell reselection, update TA/RNA location, and/ormonitor a paging channel. Mechanisms for performing initial cellselection and cell reselection are described in greater detail herein.

FIGS. 2 and 3 illustrate an initial cell selection and cell reselectionscenario. FIG. 2 illustrates a wireless communication network 200according to some embodiments of the present disclosure. The network 200may correspond to a portion of the network 100. FIG. 2 illustrates threeBSs 205 (individually labeled as 205 a, 205 b, and 205 c), three cells210 (individually labeled as 210 a, 210 b, and 210 c), and one UE 215for purposes of simplicity of discussion, though it will be recognizedthat embodiments of the present disclosure may scale to many more UEs215 and/or BSs 205. The BSs 205 are similar to the BSs 105. The UE 215is similar to the UEs 115. The BS 205 a provides service in a coveragearea or cell 210 a. The BS 205 b provides service in a coverage area orcell 210 b. The BS 205 c provides service in a coverage area or cell 210c.

As an example, at time T1, the UE 215 is activated when the UE 215 is inthe coverage of the cell 210 a. The UE 215 performs an initial cellselection procedure and camp on the cell 210 a based on channelmeasurements and certain selection criteria. While camping on the cell210 a, the UE 215 may search for a better cell 210 to camp on, forexample, due to mobility of the UE 215 (at time T2) as shown by thedashed arrow. Mechanisms for performing initial cell selection and cellreselection (e.g., mobility in idle mode) are described in greaterdetail herein.

FIG. 3 is a signaling diagram illustrating an initial cell selection andcell reselection method 300 according to embodiments of the presentdisclosure. The method 300 is employed by the network 200. The method300 is implemented by the UE 215 and the BSs 205 a, 205 b, and 205 c.Steps of the method 300 can be executed by computing devices (e.g., aprocessor, processing circuit, and/or other suitable component) of theBS 205 a, 205 b, and 205 c and the UE 215. The BSs 205 a, 205 b, and 205c may be referred to as a network. The network may further include corenetwork components, such as SGW, 5GC, and AMF entities. As illustrated,the method 300 includes a number of enumerated steps, but embodiments ofthe method 300 may include additional steps before, after, and inbetween the enumerated steps. In some embodiments, one or more of theenumerated steps may be omitted or performed in a different order.

At step 305, the UE 215 a is powered on from a power-off state. Forexample, the UE 215 a is being activated while positioned in thecoverage area of the cell 210 a at time T1 as shown in FIG. 2.

At step 310, after transitioning from the power-off state to thepower-on state, the UE 215 a scans a list of available radio frequency(RF) bands or channels. During the frequency scan, the UE 215 a measuresreceive signal quality (e.g., received signal strength indicator (RSSI))for each detected cell (or BSs 205 a, 205 b, and 205 c) on the frequencybands. For example, the BSs 205 a, 205 b, and 205 c may broadcast PSSs,SSSs, system information (e.g., MIBs and SIBs), and/or reference signalsfor respective cells 210. and the UE 215 a may determine receive signalquality from the broadcast signals. In some instances, the BSs 205 a,205 b, 205 c may operate in different frequency bands. In some otherinstances, the BSs 205 a, 205 b, 205 c may operate in the same frequencyband. In some instances, the BSs 205 a, 205 b, 205 c may use differentradio access technologies (RATs), for example, including LTE and 5G NR.In some other instances, the BSs 205 a, 205 b, 205 c may use the sameRAT. The UE 215 a may select candidate cells or BSs 205 that providereceive signal quality greater than a certain threshold. The UE 215 amay synchronize to each candidate cell and decode broadcast information(e.g., physical cell identity (PCI), public land mobile network (PLMN),TAU information) from the candidate cell.

At step 320, the UE 215 a performs a cell selection. The UE 215 a mayselect a suitable cell based on the cell information received from thefrequency scan. The UE 215 a may select a cell that belongs to a certainPLMN (e.g., a registered PLMN), not barred from access, belongs to atleast one TA that is not forbidden, and/or satisfies certain cellselection criteria (e.g., satisfying certain reference signal receivedpower (RSRP) and/or reference signal received quality (RSRQ)requirements). For example, the UE 215 a may select the cell 210 aserved by the BS 205 a. The selected cell 210 a may be referred to asthe serving cell or source cell for the UE 215 a. The scanning ofavailable frequency bands at step 310 and the cell selection step 320may be generally refer to as an initial cell selection.

At step 330, after selecting the cell 210 a, the UE 215 a may continueto acquire system information from the selected cell 210 a.

At step 340, the UE 215 a performs a random access procedure with the BS205 a. For example, the UE 215 a may exchange a random access preamble,a random access response, a RRC connection request, and a RRC connectionresponse with the BS 205 a as described above.

At step 350, after completing the random access procedure andestablishing an RRC connection with the network, the UE 215 a initiatesa network attachment procedure with the network. For example, the BS 205a may coordinate with the core network components to identify,authenticate, and authorize the UE 215 for sending and/or receiving datain the network and assign the UE 215 a with a group of TAs as describedabove. Once the network attachment procedure succeeds, a context isestablished for the UE 215 a in the network. When the network attachmentprocedure is completed, a network session is established between thenetwork and the UE 215 a. If the UE 215 a has no data to send or receiveafter the network session is established, the UE 215 a may transition toan RRC idle mode and camp on the cell 210 a.

At step 360, the UE 215 a performs an idle mode mobility procedure.While camping on the cell 210 a, the UE 215 a may monitor and evaluatereceive signal power or quality from the serving cell 210 a (e.g., theBS 205 a). When the RSRP or the RSRQ from the serving cell 210 a fallsbelow a certain threshold, the UE 215 a may monitor or evaluate receivesignal power or quality from neighboring cells (e.g., the cells 210 band 210 c) to search for a better cell for camping. In an example, theUE 215 a may identify neighboring cells based on system informationreceived from a previous cell search, or a previously camped cell,and/or monitoring from the current serving cell 210 a.

As described above, a BS may broadcast system information (e.g., MIBsand SIBs) to enable a UE to access the network. In an example, a SIBtype one (SIB1) provides scheduling information and/or availability ofother SIB types and/or information (e.g., PLMN information and/or cellbarring information) that can guide a UE in performing cell selectionand/or cell reselection. For example, the UE 215 a may search for asuitable cell based on SIB1 information received from the BS 205 a.

Some examples for the other SIB types may include a SIB type two (SIB2),a SIB type three (SIB3), a SIB type four (SIB4), and a SIB type five(SIB5). A SIB2 provides information for cell reselection that are commonfor inter-frequency cell reselection, intra-frequency cell reselection,and inter-radio access technology (inter-RAT) cell reselection. Forexample, a SIB2 may include measurement thresholds for a UE to determinewhen to start searching for another cell, cell priorities for cellreselection, and/or various cell reselection criteria and/or thresholds.A SIB3 provides neighboring cell related information for intra-frequencycell reselection. For example, the SIB3 includes physical cellidentifier (ID) information associated with an intra-frequencyneighboring cell and/or corresponding criteria for cell reselection. ASIB4 provides neighboring cell related information for inter-frequencycell reselection. For example, the SIB4 includes physical cell ID,frequency carrier, frequency band, and/or beam information associatedwith an inter-frequency neighboring cell and/or corresponding criteriafor cell reselection. A SIB5 provides neighboring cell relatedinformation for inter-RAT cell reselection. For example, the SIB5includes RAT, frequency carrier, frequency band, and/or beam informationassociated with an inter-RAT neighboring cell and/or correspondingcriteria for cell reselection. An example of an inter-RAT cellreselection may include a UE camped on an NR cell and reselecting tocamp on an LTE cell or camping. Alternatively, a UE camped on an LTEcell may reselect to camp on an NR cell. In some instances, an inter-RATcell reselection may be based on UE's preferences.

In an example, when the cell 210 b is an intra-frequency neighboringcell of the cell 210 a, the SIB3 may include information to guide a UE215 to reselect to the cell 210 b. Alternatively, when the cell 210 b isan inter-frequency neighboring cell of the cell 210 a, the SIB4 mayinclude information to guide a UE 215 to reselect to the cell 210 b. Yetalternatively, when the cell 210 b is an inter-RAT neighboring cell ofthe cell 210 a, the SIB5 may include information to guide a UE 215 toreselect to the cell 210 b.

In an example, the UE 215 may move away from the camped cell 210 a. TheUE 215 may start to search for another cell for camping when themeasured received signal power and/or the received signal quality fromthe currently camped cell 210 a falls below a certain threshold. Duringthe search, the UE 215 may measure received signal power and/or receivedsignal quality from the currently camped cell 210 a and other candidatecells (e.g., the cells 210 b and 210 c) which are qualified to beconsidered for cell reselection. For example, a candidate cell may notbe a blacklisted cell or a cell barred from access. The UE 215 may rankthe candidate cells based on certain ranking rules or cell reselectionpriorities associated with the candidate cells in addition to thechannel measurements. When the received signal power and/or the receivedsignal quality measured from any of the qualified cells becomes betterthan the currently camped cell 210 a by a certain amount (e.g., based ona hysteresis) and remains better than the currently camped cell 210 afor a predefined time duration, the UE 215 changes to camp on the bettercell.

The UE 215 may autonomously make the cell camping decision based on cellreselection criteria based on system information received from theserving cell BS 205 a. In an example, a SIB2 can include ans-IntraSearchP threshold, an s-IntraSearchQ threshold, ans-NonIntraSearchP threshold, and/or an s-NonIntraSearchQ threshold forbeginning a cell search. For example, when the received signal power ofthe currently camped cell falls below the s-IntraSearchP thresholdand/or when the received signal quality of the currently camped cellfalls below the s-IntraSearchQ threshold, the UE 215 may search and/ormonitor for an intra-frequency candidate cell. When the received signalpower of the currently camped cell falls below the s-NonIntraSearchPthreshold and/or when the received signal quality of the currentlycamped cell falls below the s-NonIntraSearchQ threshold, the UE 215 maysearch and/or monitor for an inter-frequency candidate cell or aninter-RAT candidate cell. SIB2 can also include a threshServingLowQthreshold for triggering a new cell to be reselected, a q-Hyst parameterfor the hysteresis, a Qoffset parameter for ranking intra-frequencyneighboring cells, and/or a t-Reselection timer parameter for thepredefined time duration. SIB2 can further include various measurementparameters, such as the number of SSBs to measure or average for thechannel measurements, the beam indices and/or corresponding thresholds,cell reselection priorities, and/or any other related cell reselectionconfiguration parameters as described in the 3GPP document TS 38.331Release 15, titled “3^(rd) Generation Partnership Project; TechnicalSpecification Group Radio Access Network; NR; Radio Resource Control(RRC) protocol specification,” Jan. 14, 2019, which is incorporatedherein by reference.

Referring to the example shown in FIG. 2, the UE 215 travels away fromthe cell 210 a towards the cell 210 b. At time T2, the UE 215 is closerto BS 205 b than the BSs 205 c, and thus may receive a stronger receivedsignal quality and/or a stronger received signal power from the BS 205 bthan the BSs 205 a and 205 c. The UE 215 may reselect the cell 210 b forcamping based on the channel measurements and cell reselectionparameters/criteria included in the system information received from theBS 205 a.

After reselecting to camp on the cell 210 b, the UE 215 a may acquiresystem information from the cell 210 b. The UE 215 a may wait to receiveMIBs and/or SIBs from the BS 205 b. The UE 215 a may configure varioustimers for reading MIBs and/or SIBs from the BS 205 b. When the timersfor reading the MIBs and/or SIB s expire, the UE 215 a may determinethat the UE 215 a is OOS. For example, the UE may report an OOS error toan upper layer (e.g., a network access stratum (NAS) layer), which mayin turn terminate the network session and initiate an initial cellselection procedure at the UE. In other words, the UE may return toperform the steps of 310 to 350 as shown in the method 300, wherefrequency scanning, cell selection, and network attachment areperformed. Accordingly, the declaring of an OOS upon a failure toreceive certain system information can be time consuming and canincrease power consumption at the UE. In addition, the declaring of theOOS can cause the UE to miss calls when the UE is performing the initialcell selection.

Accordingly, the present disclosure provides techniques for a UE toreselect to a different cell upon a failure to receive certain systeminformation from a selected cell instead of declaring OOS and restartingan initial cell selection. In other words, the UE may quickly reselectto another cell upon a failure to receive certain system informationfrom a currently camped cell while maintaining the same network session.The present disclosure may allow a UE to retry the fast cellreselections for a certain amount of time or a certain number ofattempts before declaring an OOS. Thus, the present disclosure can delayand reduce the occurrences of OOS errors. Accordingly, the presentdisclosure can increase the UE's in-service time and improve idle modemobility robustness.

FIG. 4 is a block diagram of an exemplary UE 400 according toembodiments of the present disclosure. The UE 400 may be a UE 115 in thenetwork 100 or a UE 215 in the network 200 as discussed above. As shown,the UE 400 may include a processor 402, a memory 404, a cell selectionmodule 408, a network module 409, a transceiver 410 including a modemsubsystem 412 and a radio frequency (RF) unit 414, and one or moreantennas 416. These elements may be in direct or indirect communicationwith each other, for example via one or more buses.

The processor 402 may include a central processing unit (CPU), a digitalsignal processor (DSP), an application specific integrated circuit(ASIC), a controller, a field programmable gate array (FPGA) device,another hardware device, a firmware device, or any combination thereofconfigured to perform the operations described herein. The processor 402may also be implemented as a combination of computing devices, e.g., acombination of a DSP and a microprocessor, a plurality ofmicroprocessors, one or more microprocessors in conjunction with a DSPcore, or any other such configuration.

The memory 404 may include a cache memory (e.g., a cache memory of theprocessor 402), random access memory (RAM), magnetoresistive RAM (MRAM),read-only memory (ROM), programmable read-only memory (PROM), erasableprogrammable read only memory (EPROM), electrically erasableprogrammable read only memory (EEPROM), flash memory, solid state memorydevice, hard disk drives, other forms of volatile and non-volatilememory, or a combination of different types of memory. In an embodiment,the memory 404 includes a non-transitory computer-readable medium. Thememory 404 may store, or have recorded thereon, instructions 406. Theinstructions 406 may include instructions that, when executed by theprocessor 402, cause the processor 402 to perform the operationsdescribed herein with reference to the UEs 115 in connection withembodiments of the present disclosure, for example, aspects of FIGS. 3and 6-11. Instructions 406 may also be referred to as program code. Theprogram code may be for causing a wireless communication device toperform these operations, for example by causing one or more processors(such as processor 402) to control or command the wireless communicationdevice to do so. The terms “instructions” and “code” should beinterpreted broadly to include any type of computer-readablestatement(s). For example, the terms “instructions” and “code” may referto one or more programs, routines, sub-routines, functions, procedures,etc. “Instructions” and “code” may include a single computer-readablestatement or many computer-readable statements.

Each of the cell selection module 408 and the network module 409 may beimplemented via hardware, software, or combinations thereof. Forexample, each of the cell selection module 408 and the network module409 may be implemented as a processor, circuit, and/or instructions 406stored in the memory 404 and executed by the processor 402. In someexamples, the cell selection module 408 and the network module 409 canbe integrated within the modem subsystem 412. For example, the cellselection module 408 and the network module 409 can be implemented by acombination of software components (e.g., executed by a DSP or a generalprocessor) and hardware components (e.g., logic gates and circuitry)within the modem subsystem 412. In some examples, a UE may include oneof the cell selection module 408 and the network module 409. In otherexamples, a UE may include both the cell selection module 408 and thenetwork module 409.

The cell selection module 408 and the network module 409 may be used forvarious aspects of the present disclosure, for example, aspects of FIGS.3 and 6-11. The cell selection module 408 is configured to performfrequency scanning upon a power-up of the UE 400, monitor for systeminformation (e.g., PSS, SSS, PBCH, MIB, SIBs, RMSI, OSI, and/or SSBs)from one or more BSs (e.g., one or more of the BSs 105 and 205) in anetwork (e.g., the network 100 or 200), search for a suitable cell forcamping based on cell information identified from the monitoring,perform a random access procedure with the BS of a selected cell,establish a network session with the network by coordinating with thenetwork module 409, and/or track and maintain cell information receivedfrom the monitoring, and/or perform idle mode mobility. The cellselection module 408 is further configured to performs the idle modemobility by evaluating signal measurements from a serving cell andneighboring cells while camping on the serving cell, performing cellreselection based on the signal measurements, performing a fast cellreselection upon failing to receive certain system information from areselected cell, maintaining a network session while performing a fastcell reselection (e.g., without declaring an OOS error), configuring atimer and/or a counter to restrict the amount of time or the number ofattempts for fast cell reselection, and/or reporting an OOS error to thenetwork module 409 when the time duration and/or the number of attemptsallowed for fast cell reselection are being exceeded, as described ingreater detail herein.

The network module 409 is configured to implement various network layerfunctions. For example, the network module 409 is configured to performa network attachment procedure with the network to establish a networksession (e.g., subsequent to an initial cell selection), monitor for anOOS error from the cell selection module 408, terminate a networksession upon receiving an OOS error from the cell selection module 408,and/or initiate an initial cell selection upon an OOS error, asdescribed in greater detail herein.

As shown, the transceiver 410 may include the modem subsystem 412 andthe RF unit 414. The transceiver 410 can be configured to communicatebi-directionally with other devices, such as the BSs 105. The modemsubsystem 412 may be configured to modulate and/or encode the data fromthe memory 404, the cell selection module 408, and/or the network module409 according to a modulation and coding scheme (MCS), e.g., alow-density parity check (LDPC) coding scheme, a turbo coding scheme, aconvolutional coding scheme, a digital beamforming scheme, etc. The RFunit 414 may be configured to process (e.g., perform analog to digitalconversion or digital to analog conversion, etc.) modulated/encoded datafrom the modem subsystem 412 (on outbound transmissions) or oftransmissions originating from another source such as a UE 115 or a BS105. The RF unit 414 may be further configured to perform analogbeamforming in conjunction with the digital beamforming. Although shownas integrated together in transceiver 410, the modem subsystem 412 andthe RF unit 414 may be separate devices that are coupled together at theUE 115 to enable the UE 115 to communicate with other devices.

The RF unit 414 may provide the modulated and/or processed data, e.g.data packets (or, more generally, data messages that may contain one ormore data packets and other information), to the antennas 416 fortransmission to one or more other devices. The antennas 416 may furtherreceive data messages transmitted from other devices. The antennas 416may provide the received data messages for processing and/ordemodulation at the transceiver 410. The antennas 416 may includemultiple antennas of similar or different designs in order to sustainmultiple transmission links. The RF unit 414 may configure the antennas416.

In an embodiment, the UE 400 can include multiple transceivers 410implementing different RATs (e.g., NR and LTE). In an embodiment, the UE400 can include a single transceiver 410 implementing multiple RATs(e.g., NR and LTE). In an embodiment, the transceiver 410 can includevarious components, where different combinations of components canimplement RATs.

FIG. 5 is a block diagram of an exemplary BS 500 according toembodiments of the present disclosure. The BS 500 may be a BS 105 in thenetwork 100 or a BS 205 in the network 200 as discussed above. A shown,the BS 500 may include a processor 502, a memory 504, a systeminformation module 508, a network module 509, a transceiver 510including a modem subsystem 512 and a RF unit 514, and one or moreantennas 516. These elements may be in direct or indirect communicationwith each other, for example via one or more buses.

The processor 502 may have various features as a specific-typeprocessor. For example, these may include a CPU, a DSP, an ASIC, acontroller, a FPGA device, another hardware device, a firmware device,or any combination thereof configured to perform the operationsdescribed herein. The processor 502 may also be implemented as acombination of computing devices, e.g., a combination of a DSP and amicroprocessor, a plurality of microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration.

The memory 504 may include a cache memory (e.g., a cache memory of theprocessor 502), RAM, MRAM, ROM, PROM, EPROM, EEPROM, flash memory, asolid state memory device, one or more hard disk drives, memristor-basedarrays, other forms of volatile and non-volatile memory, or acombination of different types of memory. In some embodiments, thememory 504 may include a non-transitory computer-readable medium. Thememory 504 may store instructions 506. The instructions 506 may includeinstructions that, when executed by the processor 502, cause theprocessor 502 to perform operations described herein, for example,aspects of FIGS. 3 and 6-11. Instructions 506 may also be referred to ascode, which may be interpreted broadly to include any type ofcomputer-readable statement(s) as discussed above with respect to FIG.4.

Each of the system information module 508 and the network module 509 maybe implemented via hardware, software, or combinations thereof. Forexample, each of the system information module 508 and the networkmodule 509 may be implemented as a processor, circuit, and/orinstructions 506 stored in the memory 504 and executed by the processor502. In some examples, the system information module 508 and/or thenetwork module 509 can be integrated within the modem subsystem 512. Forexample, the system information module 508 and/or the network module 509can be implemented by a combination of software components (e.g.,executed by a DSP or a general processor) and hardware components (e.g.,logic gates and circuitry) within the modem subsystem 412. In someexamples, the network module 509 may coordinate mobility and networkattachment functionalities with a core network in communication with theBS 500 as described herein. In some examples, a BS may include one ofthe system information module 508 or the network module 509. In otherexamples, a BS may include both the system information module 508 andthe network module 509.

The system information module 508 and the network module 509 may be usedfor various aspects of the present disclosure, for example, aspects ofFIGS. 3 and 6-11. The system information module 508 is configured totransmit broadcast system information periodically according to certainschedules to enable a UE (e.g., the UEs 115, 215, and 400) to performinitial network access, cell selection, and/or fast cell reselection, asdescribed in greater detail herein. For example, the broadcast systeminformation may include SSBs, PSS, SSS, PBCH signals, MIB, and/or SIBs.Some example SIBs that may guide a UE in performing cell selectionand/or reselection may include SIB2, SIB3, SIB4, and/or SIB5.

The network module 509 is configured to coordinate with a SWG, 5GC,and/or AMF within the core network to perform network attachmentprocedure, a TAU procedure, and/or a paging procedure with a UE.

As shown, the transceiver 510 may include the modem subsystem 512 andthe RF unit 514. The transceiver 510 can be configured to communicatebi-directionally with other devices, such as the UEs 115 and/or anothercore network element. The modem subsystem 512 may be configured tomodulate and/or encode data according to a MCS, e.g., a LDPC codingscheme, a turbo coding scheme, a convolutional coding scheme, a digitalbeamforming scheme, etc. The RF unit 514 may be configured to process(e.g., perform analog to digital conversion or digital to analogconversion, etc.) modulated/encoded data from the modem subsystem 512(on outbound transmissions) or of transmissions originating from anothersource such as a UE 115, 215, or 400. The RF unit 514 may be furtherconfigured to perform analog beamforming in conjunction with the digitalbeamforming. Although shown as integrated together in transceiver 510,the modem subsystem 512 and/or the RF unit 514 may be separate devicesthat are coupled together at the BS 105 to enable the BS 105 tocommunicate with other devices.

The RF unit 514 may provide the modulated and/or processed data, e.g.data packets (or, more generally, data messages that may contain one ormore data packets and other information), to the antennas 516 fortransmission to one or more other devices. This may include, forexample, transmission of information to complete attachment to a networkand communication with a camped UE 115 or 500 according to embodimentsof the present disclosure. The antennas 516 may further receive datamessages transmitted from other devices and provide the received datamessages for processing and/or demodulation at the transceiver 510. Theantennas 516 may include multiple antennas of similar or differentdesigns in order to sustain multiple transmission links.

In an embodiment, the BS 500 can include multiple transceivers 510implementing different RATs (e.g., NR and LTE). In an embodiment, the BS500 can include a single transceiver 510 implementing multiple RATs(e.g., NR and LTE). In an embodiment, the transceiver 510 can includevarious components, where different combinations of components canimplement RATs.

FIG. 6 is a flow diagram of a cell reselection method 600 with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure. Steps of themethod 600 can be executed by a computing device (e.g., a processor,processing circuit, and/or other suitable component) of a wirelesscommunication device or other suitable means for performing the steps.For example, a wireless communication device, such as the UE 115, UE215, or UE 400, may utilize one or more components, such as theprocessor 402, the memory 404, the cell selection module 408, thenetwork module 409, the transceiver 410, the modem 412, and the one ormore antennas 416, to execute the steps of method 600. As illustrated,the method 600 includes a number of enumerated steps, but embodiments ofthe method 600 may include additional steps before, after, and inbetween the enumerated steps. In some embodiments, one or more of theenumerated steps may be omitted or performed in a different order. Themethod 600 may be performed by a UE while in an RRC idle mode.

At step 605, the method 600 includes camping on a serving cell (e.g.,the cell 210 a). For example, the UE has previously performed an initialcell selection and network attachment using similar mechanisms asdescribed in the method 300 and may have previously camped on one ormore cells (e.g., the cells 210 b and 210 c). In other words, the UE hadestablished a network session with the network and the UE's context isknown to the network.

At step 610, the method 600 includes selecting a first candidate cellwhile camping on the serving cell. For example, the UE had acquiredneighboring cell information from system information received from apreviously camped cell or the current serving cell. The neighboring cellinformation may indicate a list of neighboring cells. The UE may makethe assumption that a neighboring cell of a previously camped cell mayalso be a neighboring cell of the current serving cell. The UE mayselect the first candidate cell from the neighboring cells based oncertain cell reselection criteria. For example, the UE selects the firstcandidate cell based on RSRPs and/or RSRQs of the serving cell and RSRPsand/or RSRQs of the first candidate cell and corresponding thresholds asdescribed above in the method 300.

At step 615, after selecting the first candidate cell, the method 600includes acquiring system information from the first candidate cell.

At step 620, the method 600 includes detecting a failure in systeminformation acquisition. For example, the UE may fail to receive and/ordecode certain critical system information. In the context of NR, thecritical system information may be referred to as mandatory systeminformation, such as MIB and SIB1. In some instances, the criticalsystem information may also include SIB2.

At step 625, upon detecting a failure in system information acquisition(e.g., fail to receive a MIB or a certain SIB), the method 600 includesdetermining whether there is any other neighboring cell available. In anexample, when the UE fails to receive information for intra-frequencyneighboring cells, inter-frequency neighboring cells, and/or inter-RATneighboring cells, the UE may monitor for intra-neighboring cells on theserving frequency. In addition, the UE may determine the availableneighboring cells based on databases of neighboring cells collected fromprevious cell monitoring history and/or geographical locationinformation of the UE. In other words, when detecting the systeminformation acquisition failure, the UE aborts the cell reselection tothe first candidate cell and searches for another neighboring cellsuitable for camping irrespective of signal measurements of the firstcandidate cell. When determining that there is another candidate cellavailable, the method 600 proceeds to step 630.

At step 630, the method 600 includes selecting a second candidate cellfrom the available candidate cells for camping while continue to camp onthe serving cell maintaining the network session. The selection of thesecond candidate cell may be different from conventional cellreselection criteria where the second candidate cell is required to havesignal measurements (e.g., RSRP and/or RSRQ) higher than signalmeasurements of the serving cell by a certain threshold (e.g.,s-IntraSearchQ, s-IntraSearchP, threshServingLowQ, and/orthreshServingLowP in SIB2) for a duration longer than a certainthreshold (e.g., t-Reselection in SIB2). The selection of the secondcandidate cell may be an immediate reselection without waiting for at-Reselection time duration. Mechanisms for reselecting the secondcandidate cell are described in greater detail herein.

At step 635, the method 600 includes determining whether the selectionof the second candidate cell is a first attempt to reselect to anothercell due to a failure in system acquisition for the first time after alast successful camping. When determining that the selection of thesecond candidate cell is a first attempt, the method 600 proceeds tostep 640.

At step 640, the method 600 includes starting a timer. For example, theUE may configure the timer with a certain expiration duration to limitthe amount of time the UE can attempt to reselect to another celltriggered by a system information acquisition failure before declaringan OOS. The expiration duration may vary depending on the embodiments.In some embodiments, the expiration duration may be about 10 seconds.

At step 645, the method 600 includes determining whether camping on thesecond candidate cell is successful. When determining that the campingon the second candidate cell is successful, method 600 proceeds to step650. The determination of whether camping on the second systeminformation is successful may include determining whether systeminformation is successfully received and decoded from the secondcandidate cell.

At step 650, the method 600 includes performing an idle mode mobilityprocedure. In other words, the second candidate cell becomes the servingcell or source cell for the UE and the UE may repeat the mobilityprocedure to monitor and evaluate the new serving cell and neighboringcells (e.g., returning to step 605). In some examples, the UE mayperform a fast or immediate cell reselection while camping on the newserving cell (e.g., the second candidate cell).

Returning to step 645, when the method 600 determines that camping onthe second candidate is unsuccessful, the method 600 proceeds to step670. At step 670, the method 600 determines whether the timer hasexpired. When determining that timer has expired, the method 600proceeds to step 665. Otherwise, the method 600 returns to step 625 torepeat the cell reselection procedure until the timer expires or the UEsuccessfully camps on a candidate cell.

At step 665, method 600 includes declaring an OOS error. For example,the UE may report an OOS error to a NAS layer and the NAS layer may inturn initiates an initial cell selection procedure at the UE.

Returning to step 635, when the method 600 determines that the selectionof the second candidate cell is not a first attempt after a lastsuccessful camping to reselect to another cell due to a failure insystem acquisition, the method 600 proceeds to step 645 to determinewhether camping on the second candidate cell is successful.

Returning to step 625, when the method 600 determines that there is nocandidate cell available, the method 600 proceeds to step 655. In otherwords, the serving cell is the only cell available and there is noneighboring cell currently available.

At step 655, the method 600 includes determining whether a serving cellmeasurement is below a threshold. In an example, the serving cellmeasurement may be an RSRQ measurement and the threshold may be similarto an s-IntraSearchQ threshold or a threshServingLowQ threshold or anysuitable threshold. In an example, the serving cell measurement may bean RSRP measurement and the threshold may be similar to ans-IntraSearchP threshold or a threshServingLowP threshold or anysuitable threshold. When determining that the serving cell measurementis below the threshold, the method 600 proceeds to step 665 to declarean OOS error. Upon declaring an OOS error, the UE may restart an initialcell selection procedure as described in the method 300 with respect toFIG. 3.

When determining that the serving cell measurement is not below thethreshold, the method 600 proceeds to step 660. At step 660, the method600 includes continuing to monitor for system information from theserving cell and returning to step 625 to repeat the cell reselectionprocedure until the timer expires or a successful camping on a candidatecell. For example, the UE may receive system information includingneighboring cell information from the serving cell in the step 660including additional neighboring cells.

In an example, the method 600 may additionally exclude a candidate cellfrom a subsequent cell selection or cell reselection if multiple systeminformation decoding failures (e.g., about three failures) are detectedfrom the candidate cell. The method 600 can identify the candidate cellbased on a global cell ID (e.g., defined in a cellldentity parameter inSIB1) of the candidate cell.

As can be observed from the method 600, upon detecting a failure toreceive certain system information, a UE may perform a fast cellreselection to select a suitable cell to camp on instead of immediatelydeclaring an OOS error (e.g., reporting to the upper layer) andrestarting an initial cell selection (e.g., including scanning offrequency bands). Accordingly, the method 600 can increase a UE'sin-service time and robustness for idle mode mobility.

FIG. 7 is a flow diagram of a cell reselection method 700 with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure. Steps of themethod 700 can be executed by a computing device (e.g., a processor,processing circuit, and/or other suitable component) of a wirelesscommunication device or other suitable means for performing the steps.For example, a wireless communication device, such as the UE 115, UE215, or UE 400, may utilize one or more components, such as theprocessor 402, the memory 404, the cell selection module 408, thenetwork module 409, the transceiver 410, the modem 412, and the one ormore antennas 416, to execute the steps of method 700. As illustrated,the method 700 includes a number of enumerated steps, but embodiments ofthe method 700 may include additional steps before, after, and inbetween the enumerated steps. In some embodiments, one or more of theenumerated steps may be omitted or performed in a different order. Themethod 700 may be performed by a UE camping on a serving cell andfailing to camp on a reselected cell (e.g., a first candidate cell). Themethod 700 may be substantially similar to the method 600, but mayutilize a counter instead of a timer to limit a duration for retrying afast cell reselection. For example, the method 700 may be suitable foruse when a UE fails to receive less critical system information from thecandidate cell. In the context of 5G or NR, less critical systeminformation may be referred to as non-mandatory system information,which may include SIB3, SIB4, SIB5, and/or other SIBs that are notrelated to uplink and/or downlink channel configuration and/or accessclass information.

At step 725, the method 700 includes determining whether there is anyother neighboring cell available while camping on a cell. Whendetermining that there is another candidate cell available, the method700 proceeds to step 730.

At step 730, the method 700 includes selecting a second candidate cellfrom the available candidate cells for camping while continue to camp onthe serving cell maintaining the network session. The selection of thesecond candidate cell may be different from conventional cellreselection criteria as described above in the step 630 of the method600.

At step 735, the method 700 includes determining whether the selectionof the second candidate cell is a first attempt to reselect to anothercell due to a failure in system acquisition for the first time after alast successful camping. When determining that the selection of thesecond candidate cell is a first attempt, the method 700 proceeds tostep 740.

At step 740, the method 700 includes resetting a counter. For example,the UE may to limit the number of attempts that the UE may attempt toreselect to another cell triggered by a system information acquisitionfailure before declaring an OOS.

At step 745, the method 700 includes determining whether camping on thesecond candidate cell is successful. When determining that the campingon the second candidate cell is successful, method 700 proceeds to step750. The determination of whether camping on the second systeminformation is successful may include determining whether systeminformation is successfully received and decoded from the secondcandidate cell.

At step 750, the method 700 includes performing an idle mode mobilityprocedure. In other words, the second candidate cell becomes the servingcell or source cell for the UE and the UE may repeat the mobilityprocedure to monitor and evaluate the new serving cell and neighboringcells. In some examples, the UE may perform a fast or immediate cellreselection while camping on the new serving cell (e.g., the secondcandidate cell).

Returning to step 745, when the method 700 determines that camping onthe second candidate is unsuccessful, the method 700 proceeds to step775. At step 775, the method 700 includes incrementing the counter.

At step 770, the method 700 determining whether the counter has exceededa maximum number of allowable attempts for fast cell reselections. Themaximum number of allowable attempts may vary depending on theembodiments. In some embodiments, the maximum number of allowableattempts may be about 3. When determining that the counter has reachedthe maximum number of allowable attempts for fast reselections, themethod 700 proceeds to step 765. Otherwise, the method 700 returns tostep 725 to repeat the cell reselection procedure until the counterreaches the maximum number of allowable attempts or a successful campingon a candidate cell

At step 765, method 700 includes declaring an OOS error. For example,the UE may report an OOS error to a NAS layer and the NAS layer may inturn initiates an initial cell selection procedure at the UE.

Returning to step 735, when the method 700 determines that the selectionof the second candidate cell is not a first attempt after a lastsuccessful camping to reselect to another cell due to a failure insystem acquisition, the method 700 proceeds to step 745 to determinewhether camping on the second candidate cell is successful.

Returning to step 725, when the method 700 determines that there is nocandidate cell available, the method 700 proceeds to step 755. In otherwords, the serving cell is the only cell available and there is noneighboring cell currently available.

At step 755, the method 700 includes determining whether a serving cellmeasurement is below a threshold. In an example, the serving cellmeasurement may be an RSRQ measurement and the threshold may be similarto an s-IntraSearchQ threshold or a threshServingLowQ threshold or anysuitable threshold. In an example, the serving cell measurement may bean RSRP measurement and the threshold may be similar to ans-IntraSearchP threshold or a threshServingLowP threshold or anysuitable threshold. When determining that the serving cell measurementis below the threshold, the method 700 proceeds to step 765 to declarean OOS error. Upon declaring an OOS error, the UE may restart an initialcell selection procedure as described in the method 300 with respect toFIG. 3.

When determining that the serving cell measurement is not below thethreshold, the method 700 proceeds to step 760. At step 760, the method700 includes continuing to monitor for system information from theserving cell and returning to step 725 to repeat the cell reselectionprocedure until the counter reaches the maximum number of allowableattempts or a successful camping on a candidate cell. For example, theUE may receive system information including neighboring cell informationfrom the serving cell in the step 760 including additional neighboringcells.

In an example, the method 700 may additionally exclude a candidate cellfrom a subsequent cell selection or cell reselection if multiple systeminformation decoding failures (e.g., about three failures) are detectedfrom the candidate cell. The method 700 can identify the candidate cellbased on a global cell ID (e.g., defined in a cellldentity parameter inSIB1) of the candidate cell.

As can be observed from the method 700, upon detecting a failure toreceive certain system information, a UE may perform a fast cellreselection to select a suitable cell to camp on instead of immediatelydeclaring an OOS error (e.g., reporting to the upper layer) andrestarting an initial cell selection (e.g., including scanning offrequency bands). Accordingly, the method 700 can increase a UE'sin-service time and robustness for idle mode mobility.

FIG. 8 is a flow diagram of a cell reselection method 800 with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure. Steps of themethod 800 can be executed by a computing device (e.g., a processor,processing circuit, and/or other suitable component) of a wirelesscommunication device or other suitable means for performing the steps.For example, a wireless communication device, such as the UE 115, UE215, or UE 400, may utilize one or more components, such as theprocessor 402, the memory 404, the cell selection module 408, thenetwork module 409, the transceiver 410, the modem 412, and the one ormore antennas 416, to execute the steps of method 800. As illustrated,the method 800 includes a number of enumerated steps, but embodiments ofthe method 800 may include additional steps before, after, and inbetween the enumerated steps. In some embodiments, one or more of theenumerated steps may be omitted or performed in a different order. Themethod 800 may be performed by a UE upon detecting a failure to receivecertain system information while camping on a serving cell andattempting to reselect a candidate cell for camping. The method 800 maybe substantially similar to the methods 600 and 700, but may utilize acombination of timer and counter to limit a duration for retrying a fastcell reselection. For example, the method 800 may be suitable for usewhen a UE fails to receive less critical system information from thecandidate cell. In the context of 5G or NR, less critical systeminformation may be referred to as non-mandatory system information,which may include SIB3, SIB4, SIB5, and/or other SIBs that are notrelated to uplink and/or downlink channel configuration and/or accessclass information.

At step 805, the method 800 includes determining whether there is anyother candidate cell available while camping on a serving cell. Whendetermining that there is another candidate cell available, the method800 proceeds to step 810.

At step 810, the method 800 includes selecting a second candidate cellfrom the available candidate cells for camping, as described in greaterdetail herein.

At step 815, the method 800 includes determining whether the selectionof the second candidate cell is a first attempt to reselect to anothercell due to a failure in system acquisition after a last successfulcamping. When determining that the selection of the second candidatecell is a first attempt, the method 800 proceeds to step 820.

At step 820, the method 800 includes starting a timer. For example, theUE may configure the timer with a certain expiration duration to limitthe amount of time the UE can attempt to reselect to another celltriggered by a system information acquisition failure. The expirationduration may vary depending on the embodiments. In some embodiments, theexpiration duration may be about 10 seconds.

At step 825, the method 800 includes resetting a counter (e.g., to avalue of 0).

At step 835, the method 800 includes determining whether camping on thesecond candidate cell is successful. When determining that the campingon the second candidate cell is successful, method 800 proceeds to step840. The determination of whether camping on the second systeminformation is successful may include determining whether systeminformation is successfully received and decoded from the secondcandidate cell.

At step 840, the method 800 includes performing an idle mode mobilityprocedure. In other words, the second candidate cell became the servingcell or source cell for the UE and the UE may repeat the mobilityprocedure to monitor and evaluate the new serving cell and neighboringcells. In some examples, the UE may perform a fast or immediate cellreselection while camping on the new serving cell (e.g., the secondcandidate cell).

Returning to step 835, when the method 800 determines that camping onthe second candidate is unsuccessful, the method 800 proceeds to step870. At step 870, the method 800 determines whether the timer hasexpired. When determining that timer has expired, the method 800proceeds to step 865. At step 865, the method 800 includes incrementingthe counter.

At step 860, the method 800 includes determining whether the counter hasexceeded a maximum number of allowable attempts for fast cellreselections. When determining that the counter has reached the maximumnumber of allowable attempts, the method 800 proceeds to step 855.

At step 855, method 800 includes declaring an OOS error. For example,the UE may report the OOS error to an upper layer (e.g. the NAS layer)and the upper layer may in turn initiate an initial cell selectionprocedure at the UE.

Returning to step 860, when determining that the counter has notexceeded the maximum allowable attempts, the method 800 proceeds to step875. At step 855, the method 800 includes starting the timer (e.g., withanother expiration duration of about 10 seconds). After the starting thetimer, the method 800 proceeds to step 805 to repeat reselecting anothercandidate cell from the neighboring cells for camping.

Returning to step 870, when determining that the timer has not expired,the method 800 proceeds to step 805 to repeat reselecting anothercandidate cell from the neighboring cells for camping.

Returning to step 815, when the method 800 determines that the selectionof the second candidate cell is not a first attempt for fast cellreselection after a last successful, the method 800 proceeds to step 835to determine whether camping on the second candidate cell is successful.

Returning to step 805, when the method 800 determines that there is noother candidate cell available, the method 800 proceeds to step 845.

At step 845, the method 800 includes determining whether a serving cellmeasurement is below a threshold. Similar to the method 600, the servingcell measurement may be an RSRQ measurement and the threshold may be ans-IntraSearchQ threshold or a threshServingLowQ threshold.Alternatively, the serving cell measurement may be an RSRP measurementand the threshold may be s-IntraSearchP threshold or a threshServingLowPthreshold. When determining that the serving cell measurement is belowthe threshold, the method 800 proceeds to step 855 to declare an OOSerror. Upon declaring an OOS error, the UE may restart an initial cellselection procedure as described in the method 300 with respect to FIG.3.

When determining that the serving cell measurement is not below thethreshold, the method 800 proceeds to step 850. At step 850, the method800 includes continuing to monitor for system information from theserving cell and returning to step 805 to repeat the cell reselectionprocedure until the timer expires or a successful camping on a candidatecell.

In an example, the method 800 may additionally exclude a candidate cellfrom a subsequent cell selection or cell reselection if multipleremaining SIB decoding failures (e.g., about three failures) aredetected from the candidate cell. The remaining SIB s or non-criticalSIBs may include any SIB other than SIB 1. The failures can be from thedecoding of any of the remaining SIBs. The method 800 can identify thecandidate cell based on a global cell ID (e.g., defined in acellldentity parameter in SIB1) of the candidate cell.

As can be observed, similar to the method 600, the method 800 allows aUE to perform a fast cell reselection upon detecting a failure toreceive certain system information from a reselected candidate cellinstead of immediately declaring an OOS error (e.g., reporting to theupper layer), which may trigger an initial cell selection (e.g.,including scanning of frequency bands), or at least delay the declaringof the OOS error and the restarting of the initial cell selection.Accordingly, the method 800 can increase a UE's in-service time androbustness for idle mode mobility.

In general, a UE (e.g., a UE 115, 215 or 400) may utilize a combinationof timer and counter, timer alone, or counter alone to limit the amountof time and/or the number of attempts the UE can perform a fast cellreselection before declaring an OOS error.

FIG. 9 is a flow diagram of a cell reselection method 900 with increaseduser in-service time and improved idle mode mobility robustnessaccording to some embodiments of the present disclosure. Steps of themethod 900 can be executed by a computing device (e.g., a processor,processing circuit, and/or other suitable component) of a wirelesscommunication device or other suitable means for performing the steps.For example, a wireless communication device, such as the UE 115, UE215, or UE 400, may utilize one or more components, such as theprocessor 402, the memory 404, the cell selection module 408, thenetwork module 409, the transceiver 410, the modem 412, and the one ormore antennas 416, to execute the steps of method 900. As illustrated,the method 900 includes a number of enumerated steps, but embodiments ofthe method 900 may include additional steps before, after, and inbetween the enumerated steps. In some embodiments, one or more of theenumerated steps may be omitted or performed in a different order. Themethod 900 may be performed by a UE upon detecting a failure to receivecertain system information while camping on a serving cell andattempting to reselect a candidate cell for camping. In an example, a UEmay perform the method 900 during step 630 of the method 600 describedabove with respect to FIG. 6, step 730 of the method 700 described abovewith respect to FIG. 7, or step 810 of the method 800 described abovewith respect to FIG. 8. For example, the UE is camped on a serving celland reselected a first candidate cell for camping. However, the UE failsto receive certain system information from the reselected firstcandidate cell.

At step 905, the method 900 includes determining whether there is anycandidate or neighboring cell satisfying a cell reselection parameter(e.g., RSRP and/or RSRQ thresholds) while camping on a serving cell. Forexample, the UE may be monitoring and evaluating one or more neighboringcells while camping on the serving cell prior to reselecting to camp onthe first candidate cell. The UE may have determined that a subset ofthe neighboring cells have receive signal measurements (e.g., RSRP orRSRQ) higher than signal measurements (e.g., RSRP or RSRQ) of theserving cell for some time periods. In other words, the neighboringcells in the subset have receive signal measurements that are qualifiedfor starting a cell reselection timer (e.g., with a t-Reselectionexpiration duration) for cell reselection evaluation. The UE maydetermine that the subset of neighboring cells satisfy the cellreselection parameter. When determining that there are one or morecandidate cells satisfying the cell reselection parameter, the method900 proceeds to step 910.

At step 910, the method 900 includes selecting a highest prioritycandidate cell from the qualified neighboring cells. In an example, thepriorities of the neighboring cells are provided by a BS (e.g., the BS105, 205, or 500) of the serving cell or a previously camped cell viabroadcast system information. Cells operating on different frequenciesand/or using different RATs may have different priorities. For example,the network may influence or encourage the UE to reselect to a certaincell over another cell by configuring a higher priority for the certaincell than the other cell.

At step 915, the method 900 includes determining whether there are morethan one candidate cells (e.g., qualifying neighboring cells) includingthe same priority (e.g., the highest priority). When determining thatthere is only one candidate cell with the highest priority, the method900 proceeds to step 935. At step 935, the method 900 includes campingon the reselected candidate cell (e.g., with the highest-priority).

Returning to step 915, when determining that there are more than onecandidate cells including the same priority, the method 900 proceeds tostep 920. At step 920, the method 900 includes selecting the candidatecell satisfying the cell reselection parameter for the longest duration(e.g., with the cell reselection timer running for the longest time) orthe candidate cell having the strongest signal strength. In someinstances, the method 900 may include a qualified cell with an expiredcell reselection timer. The method 900 may proceed to step 935 to campon the reselected candidate cell (satisfying the cell reselectionparameter for the longest time).

Returning to step 905, when determining that there is no candidate cellsatisfying the cell reselection parameter, the method 900 proceeds tostep 925. At step 925, the method 900 performs a one-shot measurementfor each neighboring cell on the same frequency and/or on differentfrequencies as the serving cell.

At step 930, after completing the one-shot measurements, the method 900includes selecting a candidate cell with at least one of the highestpriority, the highest signal measurements, or the greatest number ofbeams satisfying a certain threshold among the neighboring cells. Forexample, the UE may measure or determine an RSRP and/or an RSRQ for eachcell at the time when the failure to receive system information occurs.The UE can determine an RSRP and/or an RSRQ for each cell in each beamdirection. The UE selects the candidate cell based on the signalmeasurements and/or the cell priorities without starting a cellreselection timer. After selecting the candidate cell, the method 900proceed to step 935 to camp on the selected candidate cell.

As can be observed, the method 900 selects a highest priority cell fromneighboring or candidate cells that include valid RSRP or RSRQmeasurements satisfying cell reselection criteria (e.g., to start a cellreselection timer). When there are multiple qualified cells with thesame priority, the method 900 selects the cell with the highest signalstrength among the multiple qualified cells. It should be noted that themethod 900 selects the highest priority cell without having to wait fora certain duration (e.g., a timeout of the cell reselection timer) andwithout requiring the highest priority cell to include better signalmeasurements than the serving cell for the duration before theselection. Accordingly, the method 900 can provide a fast recovery toselect to another serving cell within a short time period (e.g., a fewseconds instead of tens of seconds as in a conventional recovery fromOOS).

When there is no neighboring cell satisfying the cell reselectionparameter, the method 900 performs a one-shot search and measurement onall neighboring cells available and reselect to the cell with thehighest priority and the highest receive signal measurements (e.g., thehighest RSRQ or the highest RSRP depending on whether threshServingLowQor threshServingLowP is configured). The method 900 may perform thereselection without starting a cell reselection timer (based on thet-Reselection parameter configured by a SIB2). Accordingly, the method900 can provide a fast recovery to reselect to another serving cellwithin a short time period (e.g., a few seconds instead of tens ofseconds as in a conventional recovery from OOS). Additionally, if arangeToBestCell parameter is defined for neighboring cells in thereceived system information, the method 900 reselects the cell with thehighest priority and the greatest number of beams having signalstrengths above a preconfigured threshold.

FIG. 10 is a time diagram illustrating a mobility scenario 1000 withfast cell reselections according to some embodiments of the presentdisclosure. The scenario 1000 may correspond to a mobility scenario of aUE, such as a UE 115, 215, or 400, in a network, such as the network 100or 200. In FIG. 10, the x-axis represents time in some constant units.The patterned filled boxes represent a successful camping on arespective cell. The boxes marked with the symbol X represent a failureto camp on a respective cell due to a failure to receive certain systeminformation (e.g., critical and/or non-critical system information). Thenetwork may include a plurality of cells 1005 similar to the cells 110and 210. The cells 1005 are shown as cell 1005 a, 1005 b, 1005 c, 1005d, 1005 e, 1005 f, and 1005 g. In the scenario 1000, the UE may employ asuitable combination of the methods 300, 600, 700, 800, and 900 for cellselection, network attachment, and reselections.

At time T0, the UE has established a network session 1002 with thenetwork and has successfully camped on the cell 1005 a as shown by 1010,for example, using the method 300. The UE may evaluate receive signalstrengths of the serving cell 1005 a and one or more neighboring cells1005 (e.g., the cells 1005 b, 1005 c, and 1005 d) while camping on thecell 1005 a.

At time T1, the UE detects that the receive signal strength of theserving cell 1005 a falls below a certain threshold and requires a cellreselection, for example, due to the UE travelling away from the servingcell 1005 a. For example, the UE detects that the neighboring cell 1005b meets certain cell reselection criteria. Thus, the UE selects the cell1005 b for camping. However, the UE fails to camp on the cell 1005 b asshown by 1020 due to a failure to receive certain system informationfrom the cell 1005 b.

Upon detecting the system information reception failure, the UE selectsanother cell for a fast cell reselection instead of declaring an OOS. Attime T2, the UE selects the cell 1005 c for camping, for example, usingthe methods 600, 700, 800, and/or 900. The UE starts a timer 1006 withan expiration duration, denoted as Td (e.g., about 10 seconds) to avoidperforming fast cell reselections indefinitely. As shown by 1030, the UEalso fails to camp on the cell 1005 c due to a failure to receivecertain system information from the cell 1005 c.

Upon detecting the system information reception failure, the UE checksthat the timer 1006 has not expired. Thus, at time T3, the UE retriesanother fast or immediate cell reselection instead of declaring an OOSerror. As shown by 1040, the UE selects the cell 1005 d and successfullycamps on to the cell 1005 d. After camping on the cell 1005 dsuccessfully, the UE stops the timer 1006 and the cell 1005 d becomesthe serving cell for the UE. As shown, the UE maintains the networksession 1002 while reselecting to the cells 1005 b, 1005 c, and 1005 d.

The UE may evaluate receive signal strengths of the currently campedcell 1005 d and neighboring cells 1005 (e.g., the cells 1005 e, 1005 f,and 1005 g) while camping on the cell 1005 d. At time T4, the UE detectsthat the receive signal strengths of the serving cell 1005 d falls belowa certain threshold and that the neighboring cell 1005 e satisfiescertain cell reselection criteria, for example, using the method 300.However, the UE fails to camp on the cell 1005 e due to a failure toreceive certain system information from the cell 1005 e as shown by1050.

Upon detecting the system information reception failure from the cell1005 e, the UE selects another cell for a fast cell reselection insteadof declaring an OOS. At time T5, the UE selects the cell 1005 f forcamping, for example, using the methods 600, 700, 800, and/or 900. TheUE starts a timer 1008 (e.g., with an expiration duration, denoted asTd, of about 10 seconds) to avoid performing fast reselectionsindefinitely. The UE also fails to camp on the cell 1005 f due to afailure to receive certain system information from the cell 1005 f asshown by 1060.

At time T6, the UE determines that the timer 1008 has not expired andretries the fast or immediate cell reselection to select to the cell1005 g instead of declaring an OOS. Again, the UE fails to camp on thecell 1005 g due to a failure to receive certain system information fromthe cell 1005 g as shown by 1070.

At time T7, the UE determines that the timer 1008 has expired (e.g., theduration 1004 exceeds the duration Td). Thus, the UE declares an OOSerror, for example, by reporting to an upper layer, such as a NAS layer.The network session 1002 may terminate upon the OOS error. The upperlayer may in turn trigger the UE to perform an initial cell selectionand establish a new network session.

FIG. 11 is a flow diagram of a cell reselection method 1100 withincreased user in-service time and improved idle mode mobilityrobustness with increased user in-service time and improved idle modemobility robustness according to some embodiments of the presentdisclosure. Steps of the method 1100 can be executed by a computingdevice (e.g., a processor, processing circuit, and/or other suitablecomponent) of a wireless communication device or other suitable meansfor performing the steps. For example, a wireless communication device,such as the UE 115, UE 215, or UE 400, may utilize one or morecomponents, such as the processor 402, the memory 404, the cellselection module 408, the network module 409, the transceiver 410, themodem 412, and the one or more antennas 416, to execute the steps ofmethod 1100. The method 1100 may employ similar mechanisms as in themethods 300, 600,700, 800, and 900 described with respect to FIGS. 3, 6,7, 8, and 9, respectively, and/or the scenario 1000 as described withrespect to FIG. 10. As illustrated, the method 1100 includes a number ofenumerated steps, but embodiments of the method 1100 may includeadditional steps before, after, and in between the enumerated steps. Insome embodiments, one or more of the enumerated steps may be omitted orperformed in a different order.

At step 1110, the method 1100 includes establishing, by a wirelesscommunication device, a network session (e.g., the network session 1002)with a wireless communication network (e.g., the network 100 or 200).

At step 1120, the method 1100 includes reselecting, by the wirelesscommunication device, a first cell (e.g., the cell 110, 210, or 1005)for camping. The first cell is associated with the wirelesscommunication network.

At step 1130, the method 1100 includes monitoring, by the wirelesscommunication device, for first system information from the first cell.In an example, the first system information may include critical systeminformation, such as MIB, SIB1, and/or SIB2. In an example, the firstsystem information may include less critical system information, such asSIB2, SIB3, SIB4, SIB5, and other remaining SIBs.

At step 1140, the method 1100 includes reselecting, by the wirelesscommunication device, a second cell (e.g., the cell 110, 210, or 1005)for camping in response to a failure to receive the first systeminformation. The second cell is associated with the wirelesscommunication network and different from the first cell.

At step 1150, the method 1100 includes maintaining, by the wirelesscommunication device, the network session during the selecting.

In an embodiment, the wireless communication device monitors one or morefrequencies for cell information, the one or more frequencies includinga first frequency associated with the first cell. The reselection of thesecond cell includes selecting the second cell from one or moreneighboring cells identified from the monitoring the one or morefrequencies for the cell information, the one or more neighboring cellsincluding the second cell.

In an embodiment, the reselection of the second cell includesdetermining, by the wireless communication device, that a subset of theone more neighboring cells include signal measurements satisfying a cellreselection parameter. The cell reselection parameter can include one ormore signal measurement thresholds for determining whether a cell isqualified to be monitored and evaluated for a cell reselection, where acell reselection timer can be started for the evaluation (e.g., based ona t-Reselection parameter in SIB2). The reselection of the second cellincludes selecting the second cell from among the subset of the one moreneighboring cells based on cell priority information associated with theone or more neighboring cells. For example, the wireless communicationdevice selects the second cell with the highest priority among the onemore neighboring cells.

In an embodiment, the reselection of the second cell further includesselecting the second cell from among the subset of one or moreneighboring cells based on at least one of the signal measurements or aduration of the signal measurements satisfying the cell reselectionparameter. For example, when there are multiple neighboring cells withthe same priority, the wireless communication device selects the secondcell with signal measurements better than signal measurements of thefirst cell for a longest duration among the multiple cells. In anembodiment, the wireless communication device performs signalmeasurements for the one or more neighboring cells in response to afailure to receive the first system information. The reselection of thesecond cell includes selecting the second cell from among the one ormore neighboring cells based on at least one of a cell priority or asignal measurement. For example, the wireless communication deviceselects the second cell with the highest priority and/or the highestsignal measurement among the one more neighboring cells.

In an embodiment, the performing can further include performing thesignal measurements for the one or more neighboring cells in a pluralityof beam directions. The selection of the second cell includes selectingthe second cell from among the one or more neighboring cells based on anumber of beams with signal measurements exceeding a threshold in theplurality of beam directions. For example, the wireless communicationdevice can select the cell including the largest number of beams withsignal measurements above a certain threshold. In an embodiment, thewireless communication device performs the measurements in response to adetermination that the one or more neighboring cells fail to satisfy acell reselection parameter.

In an embodiment, the reselection of the second cell is further based onat least one of a number of cell reselection attempts or a cellreselection duration not being exceeded. For example, the wirelesscommunication device can utilize a timer and/or a counter to limit theamount of the time the wireless communication device can spent on thefast reselection.

In an embodiment, the wireless communication device monitors for secondsystem information from the second cell in response to the selection ofthe second cell. In an embodiment, the wireless communication devicereports an 00S error for the network session in response to determiningthat at least one of the number of cell selection attempts or the cellselection duration has been exceeded.

Information and signals may be represented using any of a variety ofdifferent technologies and techniques. For example, data, instructions,commands, information, signals, bits, symbols, and chips that may bereferenced throughout the above description may be represented byvoltages, currents, electromagnetic waves, magnetic fields or particles,optical fields or particles, or any combination thereof.

The various illustrative blocks and modules described in connection withthe disclosure herein may be implemented or performed with ageneral-purpose processor, a DSP, an ASIC, an FPGA or other programmablelogic device, discrete gate or transistor logic, discrete hardwarecomponents, or any combination thereof designed to perform the functionsdescribed herein. A general-purpose processor may be a microprocessor,but in the alternative, the processor may be any conventional processor,controller, microcontroller, or state machine. A processor may also beimplemented as a combination of computing devices (e.g., a combinationof a DSP and a microprocessor, multiple microprocessors, one or moremicroprocessors in conjunction with a DSP core, or any other suchconfiguration).

The functions described herein may be implemented in hardware, softwareexecuted by a processor, firmware, or any combination thereof. Ifimplemented in software executed by a processor, the functions may bestored on or transmitted over as one or more instructions or code on acomputer-readable medium. Other examples and implementations are withinthe scope of the disclosure and appended claims. For example, due to thenature of software, functions described above can be implemented usingsoftware executed by a processor, hardware, firmware, hardwiring, orcombinations of any of these. Features implementing functions may alsobe physically located at various positions, including being distributedsuch that portions of functions are implemented at different physicallocations. Also, as used herein, including in the claims, “or” as usedin a list of items (for example, a list of items prefaced by a phrasesuch as “at least one of” or “one or more of”) indicates an inclusivelist such that, for example, a list of [at least one of A, B, or C]means A or B or C or AB or AC or BC or ABC (i.e., A and B and C).

As those of some skill in this art will by now appreciate and dependingon the particular application at hand, many modifications, substitutionsand variations can be made in and to the materials, apparatus,configurations and methods of use of the devices of the presentdisclosure without departing from the spirit and scope thereof. In lightof this, the scope of the present disclosure should not be limited tothat of the particular embodiments illustrated and described herein, asthey are merely by way of some examples thereof, but rather, should befully commensurate with that of the claims appended hereafter and theirfunctional equivalents.

What is claimed is:
 1. A method of wireless communication, comprising:establishing, by a wireless communication device, a network session witha wireless communication network; reselecting, by the wirelesscommunication device, a first cell for camping, wherein the first cellis associated with the wireless communication network; monitoring, bythe wireless communication device, for first system information from thefirst cell; reselecting, by the wireless communication device, a secondcell for camping in response to a failure to receive the first systeminformation, wherein the second cell is associated with the wirelesscommunication network and different from the first cell; andmaintaining, by the wireless communication device, the network sessionduring the reselecting the first cell for camping and the reselectingthe second cell for camping.
 2. The method of claim 1, furthercomprising: monitoring, by the wireless communication device, one ormore frequencies for cell information, the one or more frequenciesincluding a first frequency associated with the first cell.
 3. Themethod of claim 2, wherein the reselecting the second cell includes:identifying, by the wireless communication device, one or moreneighboring cells based on the monitoring the one or more frequenciesfor the cell information, the one or more neighboring cells includingthe second cell.
 4. The method of claim 3, wherein the reselecting thesecond cell includes: determining, by the wireless communication device,that a subset of the one or more neighboring cells include signalmeasurements satisfying a cell reselection parameter; and selecting, bythe wireless communication device, the second cell from among the subsetof the one or more neighboring cells based on cell priority informationassociated with the one or more neighboring cells.
 5. The method ofclaim 4, wherein the reselecting the second cell includes: selecting, bythe wireless communication device, the second cell from among the subsetof the one or more neighboring cells based on at least one of the signalmeasurements or a duration of the signal measurements satisfying thecell reselection parameter.
 6. The method of claim 3, furthercomprising: performing, by the wireless communication device, signalmeasurements for the one or more neighboring cells in response to afailure to receive the first system information, wherein the reselectingthe second cell includes: selecting, by the wireless communicationdevice, the second cell from among the one or more neighboring cellsbased on at least one of a cell priority or a signal measurement.
 7. Themethod of claim 6, wherein: the performing includes: performing, by thewireless communication device, the signal measurements for the one ormore neighboring cells in a plurality of beam directions, and thereselecting the second cell includes: selecting the second cell fromamong the one or more neighboring cells based on a number of beams withsignal measurements exceeding a threshold in the plurality of beamdirections.
 8. The method of claim 6, further comprising: determining,by the wireless communication device, that the one or more neighboringcells fail to satisfy a cell reselection parameter, wherein theperforming is in response to the determining.
 9. The method of claim 1,wherein the reselecting the second cell is further based on at least oneof a number of cell reselection attempts or a cell reselection durationnot being exceeded.
 10. The method of claim 1, further comprising:monitoring, by the wireless communication device, for second systeminformation from the second cell in response to the reselecting thesecond cell.
 11. The method of claim 1, further comprising: reporting,by the wireless communication device, an out-of-service error for thenetwork session in response to determining that at least one of a numberof cell reselection attempts or a cell reselection duration has beenexceeded.
 12. An apparatus comprising: a processor configured to:establish a network session with a wireless communication network;reselect a first cell for camping, wherein the first cell is associatedwith the wireless communication network; monitor for first systeminformation from the first cell; reselect a second cell for camping inresponse to a failure to receive the first system information, whereinthe second cell is associated with the wireless communication networkand different from the first cell; and maintain the network sessionduring the reselecting the first cell for camping and the reselectingthe second cell for camping.
 13. The apparatus of claim 12, wherein theprocessor is further configured to: monitor one or more frequencies forcell information, the one or more frequencies including a firstfrequency associated with the first cell.
 14. The apparatus of claim 13,wherein the processor configured to reselect the second cell is furtherconfigured to: identify one or more neighboring cells based on themonitoring the one or more frequencies for the cell information, the oneor more neighboring cells including the second cell.
 15. The apparatusof claim 14, wherein the processor configured to reselect the secondcell is further configured to: determine that a subset of the one ormore neighboring cells include signal measurements satisfying a cellreselection parameter; and select the second cell from among the subsetof the one or more neighboring cells based on cell priority informationassociated with the one or more neighboring cells.
 16. The apparatus ofclaim 15, wherein the processor configured to reselect the second cellis further configured to: select the second cell from among the subsetof the one or more neighboring cells based on at least one of the signalmeasurements or a duration of the signal measurements satisfying thecell reselection parameter.
 17. The apparatus of claim 14, wherein: theprocessor is further configured to: perform signal measurements for theone or more neighboring cells in response to a failure to receive thefirst system information, and the processor configured to reselect thesecond cell is further configured to: select the second cell from amongthe one or more neighboring cells based on at least one of a cellpriority or a signal measurement.
 18. The apparatus of claim 17,wherein: the processor configured to perform the signal measurements isfurther configured to: perform the signal measurements for the one ormore neighboring cells in a plurality of beam directions, and theprocessor configured to reselect the second cell is further configuredto: select the second cell from among the one or more neighboring cellsbased on a number of beams with signal measurements exceeding athreshold in the plurality of beam directions.
 19. The apparatus ofclaim 17, wherein: the processor is further configured to: determinethat the one or more neighboring cells fail to satisfy a cellreselection parameter, and the processor configured to perform thesignal measurements is further configured to: perform the signalmeasurements in response to the determining that the one or moreneighboring cells fail to satisfy a cell reselection parameter.
 20. Theapparatus of claim 12, wherein the processor configured to reselect thesecond cell is further configured to: reselect the second cell furtherbased on at least one of a number of cell reselection attempts or a cellreselection duration not being exceeded.
 21. The apparatus of claim 12,wherein the processor is further configured to: report an out-of-serviceerror for the network session in response to determining that at leastone of a number of cell reselection attempts or a cell reselectionduration has been exceeded.
 22. A non-transitory computer-readablemedium having program code recorded thereon, the program codecomprising: code for causing a wireless communication device toestablish a network session with a wireless communication network; codefor causing the wireless communication device to reselect a first cellfor camping, wherein the first cell is associated with the wirelesscommunication network; code for causing the wireless communicationdevice to monitor for first system information from the first cell; codefor causing the wireless communication device to reselect a second cellfor camping in response to a failure to receive the first systeminformation, wherein the second cell is associated with the wirelesscommunication network and different from the first cell; and code forcausing the wireless communication device to maintain the networksession during the reselecting the first cell for camping and thereselecting the second cell for camping.
 23. The non-transitorycomputer-readable medium of claim 22, further comprising: code forcausing the wireless communication device to monitor one or morefrequencies for cell information, the one or more frequencies includinga first frequency associated with the first cell.
 24. The non-transitorycomputer-readable medium of claim 23, wherein the code for causing thewireless communication device to reselect the second cell is furtherconfigured to: identify one or more neighboring cells based on themonitoring the one or more frequencies for the cell information, the oneor more neighboring cells including the second cell.
 25. Thenon-transitory computer-readable medium of claim 24, wherein the codefor causing the wireless communication device to reselect the secondcell is further configured to: determine that a subset of the one ormore neighboring cells include signal measurements satisfying a cellreselection parameter; and select the second cell from among the subsetof the one or more neighboring cells based on at least one of cellpriority information associated with the one or more neighboring cells,the signal measurements, or a duration of the signal measurementssatisfying the cell reselection parameter.
 26. The non-transitorycomputer-readable medium of claim 24, further comprising: code forcausing the wireless communication device to perform signal measurementsfor the one or more neighboring cells in response to a failure toreceive the first system information, wherein the code for causing thewireless communication device to reselect the second cell is furtherconfigured to: select the second cell from among the one or moreneighboring cells based on at least one of a cell priority or a signalmeasurement.
 27. The non-transitory computer-readable medium of claim26, wherein: the code for causing the wireless communication device toperform the signal measurements is further configured to: perform thesignal measurements for the one or more neighboring cells in a pluralityof beam directions, and the code for causing the wireless communicationdevice to reselect the second cell is further configured to: select thesecond cell from among the one or more neighboring cells based on anumber of beams with signal measurements exceeding a threshold in theplurality of beam directions.
 28. The non-transitory computer-readablemedium of claim 26, further comprising: code for causing the wirelesscommunication device to determine that the one or more neighboring cellsfail to satisfy a cell reselection parameter, wherein the code forcausing the wireless communication device to perform the signalmeasurements is further configured to perform the signal measurements isin response to the determining that the one or more neighboring cellsfail to satisfy a cell reselection parameter.
 29. The non-transitorycomputer-readable medium of claim 22, wherein the code for causing thewireless communication device to reselect the second cell is furtherconfigured to reselect the second cell based on at least one of a numberof cell reselection attempts or a cell reselection duration not beingexceeded.
 30. The non-transitory computer-readable medium of claim 22,further comprising: code for causing the wireless communication deviceto report an out-of-service error for the network session in response todetermining that at least one of a number of cell reselection attemptsor a cell reselection duration has been exceeded.